Photoresist is an organic material which is employed to define by photolithography predetermined patterns in layers of materials commonly used in the processes for fabricating semiconductor electronic devices from monocrystalline silicon wafers, for example.
In this field, the semiconductor silicon wafers are required to undergo a plurality of chemical-physical treatments directed to define complex layouts of monolithically integrated electronic circuits thereon.
Particularly where submicron patterns are to be defined, a processing technique known as plasma etching is extensively used whereby thin films of conductive and dielectric materials can be etched.
As an example, FIG. 1 of the accompanying drawings shows schematically a portion 1 of a semiconductor substrate 2 on top of which a layer or film 3 of a plasma etch-susceptible material, e.g., a dielectric layer, a layer of polycrystalline silicon, or a metallization layer, has been deposited. A protective mask 4, e.g., of a photoresist, is provided on top of this layer 3 to be etched.
In order to define patterns in the film 3 protected by the mask 4, the semiconductor must be subjected to a plasma etching step that will remove some of the film 3 material, through openings made in the mask 4.
After the end of the plasma etching step, as shown in FIG. 2, the photoresist mask 4 must be removed. Removing the photoresist mask 4 uncovers the patterns of the finished product as shown in FIG. 3.
The mask 4 removal is usually effected by subjecting the wafer to a second plasma or wet treatment which is selective enough to remove the mask of organic material without affecting the layers underneath.
Removing the protective mask 4 is often a fairly lengthy procedure.
As the technology progresses, the number of films or layers wherein patterns are to be defined tends to increase with the complexity of the microelectronic device. Consequently, the removal of the photoresist mask is a reiterative process that is carried out several times for each etched layer in the course of the device fabrication.
There is, therefore, a growing demand for techniques which allow the protective mask to be removed as effectively and rapidly as possible.
The prior art techniques have been directed to fill this demand by developing more aggressive removal processes and at the same time optimizing the parameters involved in the process, such as pressure, temperature, the type of reactant employed, etc.